1. Field of the Invention
The present invention relates generally to a method for manufacturing metal interconnects, and more particularly, to a method for manufacturing metal interconnects capable of reducing dishing effect.
2. Description of the Prior Art
In the fabrication of semiconductor integrated circuits (ICs), semiconductor devices are generally connected by several metallic interconnecting layers commonly referred to as multi-level interconnects, and damascene process has been deemed a convenient and predominant method for forming the multi-level interconnects. Principally, the damascene process includes etching a dielectric material layer to form trench and/or via hole patterns, filling the patterns with conductive materials such as copper, and performing a planarization process. Thus metal interconnects are obtained.
Chemical mechanical planarization, or chemical mechanical polishing (hereinafter abbreviated as CMP), is a common technique used in the planarization process. Those skilled in the art have well known that the topography and pattern densities of the surface being polished influence CMP result greatly. When planarizing structures comprised of different film layers using CMP, it is desirable for the final structure to exhibit coplanarity with respect to each film. However, “dishing”, which is the formation of topographical defects, such as concavities or depressions, in the copper and copper alloy layer of features formed on the substrate surface, is often found. Dishing issue further results in a non-planar surface that impairs the ability to print high resolution lines during subsequent photolithographic steps and detrimentally affects subsequent surface topography of the substrate and device/line formation. Furthermore, dishing issue also detrimentally affects the performance of devices by lowering the conductance and increasing the resistance of the devices, contrary to the benefit of using higher conductive materials, such as copper.
Since CMP process is one accepted method of planarization and now typically employed in the industry, it is always in need to solve the inferior evenness and to diminish dishing issue.